* {
  margin: 0;
  padding: 0;
  list-style: none;
}



.bannerBox {
  position: relative;
  width: 900px;
  height: 300px;
  /* box-shadow: 0 0 10px gray; */
  margin: 10% auto 0 auto;
  border-radius: 5px;
  overflow: hidden;
  /* background-color: rgb(0, 0, 0, .8); */


}

#banner {
  list-style: none;
  position: absolute;
  padding: 0;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  margin: auto;
  width: 800px;
  height: 200px;
}


#banner:hover {
  cursor: pointer;
}


#banner li {
  float: left;
  position: absolute;
  left: 0px;
  transition-duration: 1s;
}

#banner li img {
  width: 400px;
  height: 200px;
}

#btn {
  opacity: 0;
  transition: all .5s;
}

#btn li {
  position: absolute;
  top: 50%;
  width: 18px;
  height: 18px;
  border-top: 3px solid rgba(255, 255, 255, .6);
  border-right: 3px solid rgba(255, 255, 255, .6);
  z-index: 100;
  cursor: pointer;

}

.bannerBox:hover #btn {
  opacity: 1;
}

#btn li:Hover {
  border-color: white;
}

.prev {
  left: 15px;
  transform: rotate(-135deg);
}

.next {
  right: 15px;
  transform: rotate(45deg);
}